1. Field of the Invention
The present invention relates to a method for producing an image-forming apparatus while keeping the inside in a pressure-reduced state. Particularly, the invention relates to a method for producing the image-forming apparatus while wires used in the image-forming apparatus are formed by sintering particles of an electric conductor. The invention further concerns the image-forming apparatus produced using the production method.
2. Related Background Art
Cathode-ray tubes (CRTs) are popularly and generally used as the image-forming apparatus at present. Recently, the large cathode-ray tubes with the display screen over 30 inches also came on the market. In order to increase the size of the display screen in the case of the cathode-ray tubes, however, there arise problems that the depth dimension thereof must be increased according to the increase of the screen size and that the weight also becomes greater according to the increase of the screen size.
In order to meet the consumer""s desires for images of strong appeal on a larger screen, the cathode-ray tubes thus require a larger placement space and thus are not always suitable for realizing the increase of the screen size.
There are thus expectations for the debut of a flat image display apparatus that is thin enough to be hung on a wall, that is of low power consumption, and that has a thin, lightweight, large screen, in place of the large and heavy cathode-ray tubes (CRTs). Research and development is active on liquid-crystal display devices (LCDs) as such flat image display apparatus.
Since the above LCDs are not of an emissive type, they require a light source called a back light. They thus had a problem that most of the power consumption was due to lighting of the back light. Further, the LCDs still have problems that the image is dark because of low utilization efficiency of light, there is a limit to viewing angles, it is difficult to realize a large screen over 20 inches, and so on.
An emissive type flat image display apparatus is thus drawing attention instead of the LCDs having the above problems. Examples of such display apparatus proposed heretofore are, for example, plasma display panels (PDPs) arranged to emit light by irradiating a fluorescent material with ultraviolet light to excite the fluorescent material, flat panel displays arranged to emit light by irradiating the fluorescent material with electrons emitted from electron-emitting devices to excite the fluorescent material, and so on.
With the displays using the electron-emitting devices, the fluorescent material is made to emit light when the fluorescent material is irradiated with electrons emitted from the devices under reduced pressure. Therefore, the light emission mechanism thereof is thus basically the same as in the case of the CRTs. This permits us to expect high-luminance displays without viewing angle dependence.
Such electron-emitting devices are generally classified into cold cathodes and thermionic cathodes. Further, the cold cathodes include field emission type electron-emitting device (hereinafter referred to as xe2x80x9cFExe2x80x9d), electron-emitting device comprised of a stack of metal layer/insulating layer/metal layer (hereinafter referred to as xe2x80x9cMIMxe2x80x9d), surface conduction electron-emitting device, and so on.
In the image display apparatus using the above electron-emitting devices, the devices need to operate in an airtight vessel maintained, for example, under a pressure lower than 10xe2x88x924 Pa.
The image display apparatus using the surface conduction electron-emitting devices among the above cold cathode is disclosed, for example, in Japanese Patent Applications Laid-Open No. 6-342636, No. 7-181901, No. 8-034110, No. 8-045448, No. 9-277586, and so on.
FIG. 5 and FIG. 6 show the schematic structure of an example of the surface conduction electron-emitting devices disclosed in the above applications. FIG. 7 is a diagram to show the schematic structure of an example of the image display apparatus using the surface conduction electron-emitting devices disclosed in the above applications.
FIG. 5 is a plan view of the surface conduction electron-emitting device and FIG. 6 is a cross-sectional view of the surface conduction electron-emitting device. In FIG. 5 and FIG. 6, reference numeral 101 designates an insulating substrate, 104 an electroconductive film, 102 and 103 electrodes, and 105 an electron-emitting region. The electron-emitting region 105 has a gap. When a voltage is placed between the electrodes 102, 103, the electron-emitting region 105 emits electrons.
In FIG. 7 numeral 5005 denotes a rear plate, 5006 an outer frame, and 5007 a face plate. Joint (Sealing) portions between the outer frame 5006, the rear plate 5005, and the face plate 5007 are joined (or sealed) to each other with a bonding material such as a low-melting-point glass frit or the like not illustrated, thereby composing an airtight vessel 170 for maintaining the inside of the image display apparatus in vacuum. The surface conduction electron-emitting devices 5002 are formed in an array of Nxc3x97M on the rear plate 5005 (where N and M are positive integers not less than 2 and are properly determined according to the number of display pixels aimed). A fluorescent material is opposed to the electron-emitting devices.
The electron-emitting devices 5002 are wired in a matrix by M column-directional wires 107 and N row-directional wires 106, as illustrated in FIG. 7. In the case of this wiring in the matrix, insulating layers, not illustrated, are placed for electrically insulating the two types of wires from each other, at least, at intersecting portions between the row-directional wires and the column-directional wires.
A fluorescent film 5008 comprised of the fluorescent material is formed on the lower surface of the face plate 5007. A metal back 5009 of Al or the like is formed on the rear-plate-side surface of the fluorescent film 5008.
In the case of color display, fluorescent materials (not illustrated) of the three primary colors, red (R), green (G), and blue (B), are laid separately. Further, a black material (not illustrated) is laid between the fluorescent materials of the respective colors forming the fluorescent film 5008.
The inside of the above airtight vessel is maintained in a vacuum of the pressure lower than 10xe2x88x924 Pa. The distance between the rear plate 5005 with the electron-emitting devices formed thereon and the face plate 5007 with the fluorescent film formed thereon, as described above, is usually kept in the range of several hundred xcexcm to several mm.
A method for driving the image-forming apparatus described above is as follows. A voltage is applied to each electron-emitting device 5002 via terminals Dx1 to Dxm, Dy1 to Dyn outside the vessel, and via the wires 106, 107, whereby each device 5002 emits electrons. At the same time as it, a high voltage of several hundred V to several kV is applied to the metal back 5009 via a terminal Hv outside the vessel. This accelerates the electrons emitted from each device 5002 to make them collide with the corresponding fluorescent material of each color. On this occasion the fluorescent material is excited to emit light, thus displaying an image.
In recent years there are needs for further increase of the screen size in the image-forming apparatus. In order to produce the image-forming apparatus of several ten inches at low cost, it is then desirable to form the above wires by a sintering method (for example, a printing method) of applying conductive particles onto a substrate and baking them. Printing methods, particularly screen printing methods, are preferable, because wires of a thick film can be produced at low cost thereby.
Incidentally, in the image-forming apparatus using the electron-emitting devices, the members (the outer frame 5006, the face plate 5007, and the rear plate 5005) forming the airtight vessel 170 are joined (sealed) to each other through the bonding material (for example, the frit glass or the like). The wires (5004, 5003) for driving the devices play a role of supplying the voltage to each device in the airtight vessel from a voltage generating source placed outside the airtight vessel 170. Therefore, the wires for driving the devices pass through the sealed area of the airtight vessel. The wires existing in the joint (sealed) part thus also function to maintain the vacuum in the airtight vessel 170 in cooperation with the bonding material.
On the other hand, the wires formed by the printing method are usually produced in such a way that a paste is prepared by blending particles of the electric conductor (for example, metal powder), a binder, a solvent, etc., the paste is applied onto the substrate, and then it is baked to remove the binder and the like.
The wires formed by the above method are thus aggregates (sintered bodies) of the particles of the conductor (for example, metal) and low packing density in some cases. The packing density herein is specifically the distance of clearance and existence of gap between the particles of the conductor (for example, metal) approximately.
Speaking of the airtight vessel 170 illustrated in FIG. 7, where the wires passing through the joint (sealed) part between the outer frame and the glass substrate (5007 or 5005) are formed by the above method, the existence of many clearances described above will cause the pressure to gradually increase inside the airtight vessel 170. In the worst case, the image-forming apparatus using the electron-emitting devices, which require the high vacuum, would fail to operate because of the increase of the pressure.
In the image-forming apparatus having the matrix of wires formed as illustrated in FIG. 7, the column-directional wires 107 are formed on the rear plate 5005. The insulating layers are formed on the column-directional wires 107, at least, at the intersecting portions between the row-directional wires 106 and the column-directional wires 107. Then the row-directional wires are formed continuously on laminates of the insulating layers and the column-directional wires and on the rear plate. Consequently, the row-directional wires are formed in greatly stepped portions, different from the column-directional wires formed on the nearly flat surface. There were cases wherein the position accuracy of the row-directional wires was degraded and wherein electric connections became poor at the step portions.
An object of the present invention is, therefore, to restrain a vacuum leak which is assumed to be caused by the structure of the wires at the joint part (sealing part) of the airtight vessel described above. Another object of the invention is to form the wires with accuracy and good electric connections at the step portions. A further object of the invention is to provide a method for producing the airtight vessel that can maintain a high vacuum over a long period, without increase of the time necessary for production steps of the airtight vessel. Still another object of the invention is to provide an image-forming apparatus that can form stable images over a long period.
In order to accomplish the above objects, the present invention comprises the following:
a method for producing an image-forming apparatus comprising an airtight vessel in which a rear plate having an electron-emitting device and a wire connected to the device, and a face plate having an electrode are joined (sealed) to each other through a bonding material, said method comprising a first step of forming a first wire which is a part of said wire and which passes through said sealing part to connect the inside of said vessel to the outside, by applying a paste comprising particles of an electric conductor and baking the paste, and a second step of forming a second wire located in said vessel, by applying a paste comprising particles of an electric conductor so as to be connected to the first wire inside said vessel and baking the paste, after formation of said first wire.
In the production method according to the present invention, the wire located in the joint (sealing) part can be baked for a long time. As a result, the leak is restrained at the joint (sealing) part, so that stable image formation can be carried out over a long period.
The present invention is further characterized in that the wire comprises a plurality of row-directional wires extending in a row direction and a plurality of column-directional wires extending in a direction substantially perpendicular to the row direction and electrically insulated from the row-directional wires and in that the row-directional wires are formed by the first step and the second step. The invention is also characterized in that the column-directional wires are formed in the same step as the first step of forming the row-directional wires.
The formation of the matrix wires in this way can assure a long baking time of the wires located at the joint (sealing) part (i.e., takeout portions) without substantially increasing the number of steps for formation of the wires.
The present invention is also characterized in that the insulating layer is formed in a pattern of lines extending in the row direction and is formed so as to be connected to parts of the row-directional wires formed in the first step. The present invention is further characterized in that the thickness of the row-directional wires is greater than that of the column-directional wires.
The formation in this way can restrain occurrence of discontinuity or an electrical connection failure at the step portions of the row-directional wires.
The present invention is also characterized in that the electron-emitting device comprises a first electrode and a second electrode and in that the method further comprises a step of forming the first electrode and the second electrode, prior to said first step.
The formation in this way can make securer the electric connections between the wires and the electron-emitting device.